Engineering components, particularly rotating components such as turbine fan blades, compressor blades, impellers, blisks, and integrally bladed rotors (IBRs), commonly encounter vibrational stresses in operation. These vibrational stresses can fatigue the component and eventually cause the component to fail. In order to prevent component failure, researchers have investigated a number of approaches for attenuating the vibrations that develop under cyclic loading. Such approaches have included dry friction dampers, tuned-mass or particles, air cavities, shape memory alloys, viscoelastic dampers, and ceramic coatings. Another approach that has been considered for vibration damping is the application of a thin coating of a ferromagnetic material on a surface of a substrate. Examples of ferromagnetic materials are Fe alloys including combinations of one or more Al, Mo and Mn and Co alloys including combinations of one or more Ni, Cr, Mn, and Si. In particular, Fe—Cr based ferromagnetic materials comprising about 16% (by weight) chromium (Cr), either about 1% to about 6% aluminum (Al) or about 1% to about 4% molybdenum (Mo), and the balance iron (Fe), have been shown to exhibit high damping, as well as good mechanical strength and corrosion resistance. As a result, the ferromagnetic materials are considered well-suited for applications involving severe and hostile operating conditions, such as those experienced by turbine components. There are several drawbacks to prevent application of ferromagnetic materials for vibration damping enhancement. These drawbacks include: (I) ferromagnetic damping may be constrained by residual stresses during the coating processes; and (II) ferromagnetic damping is strain dependent and usually reaches to the maximum value at very low strain levels and quickly decays to low damping at high strain regions.
As mentioned, Fe—Cr based ferromagnetic materials have been shown to possess a high damping capacity. These ferromagnetic materials include magnetic domains, which are separated by magnetic domain walls. When the ferromagnetic material is exposed to external magnetic fields or stresses, the magnetic domain walls can move. When the movement of the magnetic domain walls is irreversible, a portion of the energy provided to the ferromagnetic material is dissipated as internal friction. This damping mechanism is commonly referred to as magnetomechanical damping. Thus, high damping in ferromagnetic materials is achieved due to the irreversible movement of the magnetic domain walls. If movement of the magnetic domain walls is constrained or hindered, the ferromagnetic material will not exhibit any appreciable damping. Unfortunately, conventional coating processes may create large residual stresses that act as obstacles to the movement of the magnetic domain walls. For example, in a conventional air plasma spray process, the residual stress is dominated by tensile quenching stresses; while in a conventional cold spray process, the residual stress is dominated by compressive peening stresses. As a result, a ferromagnetic coating applied to a substrate by conventional coating processes will provide no significant damping. In order to free up the movement of the magnetic domain walls, the common course of action is to subject the coated article to a high temperature annealing process. For example, one commonly suggested process includes an annealing process in a high vacuum at temperatures between 900° C. to 1200° C. for 6 hours. Such a high temperature annealing process is a critical drawback that has hindered the use of ferromagnetic materials in real world applications. For example, high temperature annealing of geometrically complex structural components, such as gas turbine engine components, can cause microstructural defects, decomposition, and precipitation in component substrate materials. Further, such high temperature annealing may warp or deform the structural component rendering the component unfit for its intended use. Thus there is a need in the art for a process capable of depositing a coating comprising a ferromagnetic damping material on a surface of a substrate without requirement of high temperature heat treatment.
The dependency of the strain or stress amplitude and the damping capability (characterized as loss factory η or Q−1) of ferromagnetic materials have been carefully evaluated. A number of vibration modal analyses/tests have been conducted on a flat polished beam specimen, made substantially entirely from the ferromagnetic material with composition contain of a mixture of Fe and Cr, and an active ingredient of Al or Mo. The weight ratios of Fe—Cr—Al or Mo are Fe-16% Cr-0% Al or Mo to Fe-16% Cr-6% Al or Fe-16%-4% Mo. As shown in FIG. 6, high damping capability and the damping dependence of the applied strain was obtained based on the experimental data at the first bending mode of a beam made entirely of the BCC Fe—Cr based ferromagnetic materials/alloys named as “low strain.” The frequency response results clearly show that the damping capacity of the coating specimen improves as the forcing acceleration increases. However, the damping increases rapidly as the forcing accelerations increases and reaches a stationary value as the maximum strain of the beam approaching 80 to 100 micro-strains and then decreases relatively quickly at higher strain regions. Fatigue failure in real turbine hardware is usually occurs under high strain or stress operating conditions. Therefore, there is a need in the art for a new ferromagnetic material capable of providing high damping at high strain regions. Thus there is a need in the art for a process capable of depositing a coating comprising a face-centered cubic ferromagnetic damping material on a surface of a substrate that exhibits a high damping capacity, particularly at high strain levels, without having to undergo a high temperature annealing process.